1. Field of the Invention
The present invention relates to a radio communication apparatus included in each of a plurality of radio systems which share a frequency band, and a program.
2. Description of the Related Art
Conventionally, there is known a radio communication apparatus included in each of a plurality of radio systems which share a frequency band. According to conventional radio communication apparatuses of this type, a radio communication apparatus with low priority performs carrier detection within a shared frequency band, and transmits a signal when determining that the shared frequency band is not used by a radio system with high priority (see, for example, J. Mitola III, “Cognitive Radio for Flexible Mobile Multimedia Communications”, IEEE Sixth International Workshop on Mobile Multimedia Communications (MoMuC99), pp. 3-10, No. 1999).
Conventionally, there is known a technique of reducing interference given to another radio communication system using the same frequency band and also reducing characteristic deterioration due to interference given from another system (see, for example, JP-A 2001-298763 (KOKAI)).
According to the above conventional technique, when a base station detects by carrier sense that there is no radio station which does not belong to the self radio communication system, the base station transmits an idle signal as a signal notifying that a communication channel is available to a terminal. Upon receiving the idle signal, the terminal transmits a desired communication packet to the base station. In this case, the base station at its current position detects that the communication channel is available, but the terminal at its current position does not detect that the communication channel is available. For this reason, a signal transmitted from the terminal interferes with a radio station which does not belong to the self radio communication system.